A technique of fabricating an RGB-type multicolor light-emitting lamp by adjacently disposing light-emitting diodes (LED) capable of emitting each color of red light (R), green light (G) and blue light (B) which are the three primary colors of light has been heretofore known. For example, a technique of fabricating an RGB-type multicolor light-emitting lamp by integrating an LED (blue LED) of emitting blue band light having a light emission wavelength of 450 nm, a green LED of emitting green band light having a light emission wavelength of around 525 nm and a red LED of emitting red band light having a light emission wavelength of approximately from 600 to 700 nm is known (see, Display Gijutsu (Display Technique), 1st ed., 2nd imp., pages 100 to 101, Kyoritsu Shuppan (Sep. 25, 1998)).
Conventionally, a multicolor light-emitting lamp is fabricated by using a GaXIn1-XN-base blue LED (see, JP-B-55-3834) where the light-emitting layer is composed of a group III-V compound semiconductor such as gallium indium nitride (GaXIn1-XN: 0≦X≦1) (see, III Zoku Chikkabutsu Handotai (Group III Nitride Semiconductor), pages 252 to 254, Baifukan (Dec. 8, 1999)). For the green LED, a GaXIn1-XN green LED or a homo-junction type GaP green LED, which has gallium phosphide as a light-emitting layer, is used (see, (1) III Zoku Chikkabutsu Handotai (Group III Nitride Semiconductor), pages 249 to 252, supra, and (2) III-V Zoku Kagobutsu Handotai (Group III-V Compound Semiconductor), 1st ed., pages 253 to 261, Baifukan (May 20, 1994)). For the red LED, an LED having a light-emitting layer composed of a group III-V compound semiconductor such as aluminum gallium arsenide mixed crystal (AlXGa1-XAs: 0<X<1) or aluminum gallium indium phosphide ((AlXGa1-X)YIn1-YP: 0≦X≦1, 0<Y<1) is used (see, Iwao Teramoto, Handotai Device Gairon (Outline of Semiconductor Device), pages 116 to 118, Baifukan (Mar. 30, 1995)).
Also, it is known that white light can be obtained by mixing complementary colors, for example, blue band light and yellow band light (see, Hikari no Enpitsu-Hikari Gijutsusha no tame no Oyo Kogaku-(Pencil of Light-Applied Optics for Optical Engineer), 7th ed., page 51, Shin Gijutsu Communications (Jun. 20, 1989)). For the yellow LED suitable to be combined with the blue LED, a homo-junction type GaAsP-base LED comprising a gallium arsenide phosphide (GaAs1-ZPZ: 0<Z<1) light-emitting layer having a light emission wavelength of about 590 nm, and an aluminum gallium indium phosphide mixed crystal ((AlXGa1-X)YIn1-YP: 0≦X≦1, 0<Y<1 generally Y=about 0.5) hetero-junction type LED can be suitably used (see, J. Crystal Growth, 221, pages 652 to 656 (2000)).
The gallium indium nitride (GaXIn1-XN (0≦X≦1))-base LED constituting a multicolor light-emitting lamp is usually fabricated using an electric insulating sapphire (α-Al2O3 single crystal) as the substrate material (see, III Zoku Chikkabutsu Handotai (Group III Nitride Semiconductor), pages 243 to 252, supra). Since a current (operating current) for driving the LED cannot be passed through the insulating crystal substrate, both of positive and negative electrodes are disposed in the same surface side of the substrate. On the other hand, the homo-junction type GaP-base or homo-junction type GaAs1-ZPZ-base LED is fabricated by using an electrically conducting gallium phosphide (GaP) single crystal or gallium arsenide (GaAs) single crystal and therefore, only one electrode having either positive polarity or negative polarity is disposed in the surface side (see, Handotai Device Gairon (Outline of Semiconductor Device), page 117, supra).
In any case, when an RGB three color integration-type white lamp is fabricated by using conventional GaXIn1-XN (0≦X≦1)-base blue, green and red LEDs each comprising an insulating crystal substrate, both electrodes of positive polarity and negative polarity are disposed on the surface of each LED, therefore, wire bonding to electrodes of one polarity and wire bonding to electrodes of another polarity must be separately performed and this is cumbersome. If the polarity of the electrodes to be bonded can be unified to either positive or negative by making use of an electrically conducting substrate, particularly an electrically conducting substrate having the same conductivity, the cumbersome bonding can be avoided.
In recent years, a technique of fabricating a blue LED by using a boron-containing group III-V compound semiconductor layer and a light-emitting layer composed of a group III-V compound semiconductor, which are provided on an electrically conducting silicon single crystal (silicon), is disclosed (see, U.S. Pat. No. 6,069,021). If a blue LED using an electrically conducting substrate having the same conductivity as the substrate used for the fabrication of a green or red LED is used, an RGB-type multicolor light-emitting lamp can be readily fabricated without incurring cumbersome bonding operation as in conventional techniques.
On the other hand, the GaP-base or GaAs1-ZPZ-base LED constituting the multicolor light-emitting lamp together with the GaXIn1-XN-base blue LED has a homo-junction type structure. Therefore, the light emission intensity of the GaP-base or GaAs1-ZPZ-base LED is lower than that of the GaXIn1-XN (0≦X≦1) double hetero (DH)-junction type LED, failing in providing a multicolor light-emitting lamp well-balanced in view of the light emission intensity. If a hetero-junction type structure capable of exerting a “confinement” effect on carrier to cause light emission by radiation recombination is formed, this is expected to bring higher intensity light emission.
The present invention provides a technique for fabricating a multicolor light-emitting lamp by using a blue LED having a structure capable of avoiding cumbersome bonding. In particular, the present invention provides a technique for fabricating a multicolor light-emitting lamp by using a hetero-junction type GaP-base LED capable of emitting high intensity green light in combination. Also, for example, in fabricating a multicolor light-emitting lamp from the blue LED and the yellow LED, the present invention provides a technique for fabricating a multicolor light-emitting lamp from a blue LED requiring no cumbersome bonding and a hetero-junction type GaAs1-ZPZ-base yellow LED of emitting light having high light emission intensity. Furthermore, the present invention provides a light source fabricated from the multicolor light-emitting lamp according to the present invention.